1. Field of the Invention
This invention pertains to flow control valves and particularly to a combination shut off and check valve.
2. Description of the Prior Art
Liquid which is either stored or in a flowing state through a transmission line must be handled or diverted and/or monitored at one or more stages or points. Such points occur at junctions or terminals and often utilize a valve to perform an operation with respect to the liquid at the point. As an example, it is common to employ a liquid sight monitor in a liquid transmission line so that the condition of the liquid in the line can be observed. A valve is generally located upstream of the sight monitor so that flow can be shut off in order to clean or replace the sight monitor when such maintenance need arises.
Although a valve for the above purpose can take the form of many shapes, a common valve type is a ball valve. A typical ball valve includes a ball closure located in the housing of the valve. The ball closure has a flow hole therethrough having approximately the same or smaller internal diameter as the bore through the valve housing. Such housing bore, in turn, has approximately the same internal diameter as the internal diameter of the transmission line. Hence, when the ball is swiveled so that the flow hole through the ball closure is aligned with the bore of the housing, there is a continuous flow passage through the valve. When the ball closure is rotated or swiveled in its housing by 90 degrees from its open position, the passage through the valve is blocked or shut off.
Another type of valve that is employed in liquid storage or transmission systems is a check valve. Such a valve normally includes a valve seat around a port in line with the transmission line and a ball or other shape closure that mates with the seat. Predominant liquid flow is in a direction opposing the closure. When the flow pressure falls below a predetermined level, an opposing spring, gravity or pressure differential action causes the closure to automatically seat with the valve seat to thereby positively close the valve.
Turning again to the example of a liquid sight monitor, if the glass breaks or the seals around the device should give way so as to cause a breach, the liquid contents of the adjoining transmission line or storage tank will spill out through the breach unless there is a check valve in place to prevent this from happening. A check valve, as noted above, is an automatically operating valve and is not one that is normally externally manipulable.
If it is desirable to have both a shut off valve and a check valve at the same location, it has been necessary to employ two separate valves or at least valve structures, although perhaps both could be located in serial in a common housing. A simple combination valve has not been available.
Therefore, it is a feature of the present invention to provide an improved valve combining in a single, simplified structure the functions of both a shut off valve and a check valve.